The light intensity of conventional lamps is mainly controlled by their input current. Therefore, a dimmable lamps based on the conventional technique which was utilizing an AC light dimmer to modulate the phase of input AC voltage then output a phase-modulating AC voltage. Users can use a control device on the AC light dimmer to control the alternating light dimmer, modulate the phase of AC voltage, and enable the phase-modulating AC voltage for dimming brightness or intensity.
The brightness of the lamp is determined by the output phase-modulating AC voltage from the AC light dimmer. If the voltage level becomes lower after modulating the phase of the AC voltage, the light intensity of the lamp will become dimmer; on the contrary, if the voltage level becomes higher, the light intensity of the lamp will become brighter
Nowadays, LED lighting devices has gradually replaced the conventional light bulbs or lamps, the brightness of the LEDs is proportional to their induced current. As a consequence, to adjust the current output from the LED driving device to the LED will regulate the output light intensity. However, the ways of driving conventional light lamps are different from the LED lighting devices. It is not easy for users to regulate the intensity of the LED lighting devices, so the conventional way of using AC light dimmer is not suitable for operating the LED lighting devices.
Typical prior art, phase-modulating LED driver with flyback converter can only allow the usage of input/output capacitors with small capacity for phase-modulating light dimming. The main drawback of the usage of input/output capacitors with small capacity is that the output ripple current will cause the LEDs overheated and shorten their lifetime, even further result an unstable output and led to light flicking.
Accordingly, a modification of the above LED driver circuit remains needed for increasing input/output capacitance and reducing the output ripple current of the LEDs.